Current computerized display technologies represent data which varies temporarily or spatially much the same way that mechanical methods have been used for many years. Examples of such previous mechanical approaches are illustrated by using a pen to record a variable on a moving piece of paper. These apparatus, for example, may involve the variation of a stylus along a first display axis while the paper beneath the stylus is moved at a metered rate along a second axis. Thus a two axis, two dimensional representation of data is produced. The output of these mechanical display apparatus and methods is a continuous line which varies along one axis to indicate the value of the entity being recorded by the stylus (e.g. the instantaneous temperature of a location) while showing the temporal or spatial variations of the data along a second, moving axis (e.g. per hour). These mechanical display apparatus and methods are limited, however, in that only a small number of display entities can legibly be shown along the stationary display axis. Further, the data's variation along the moving axis is limited by typical lengths of usable paper and/or screen display areas, particularly where the range of temporal or spatial data variation is large or where a large quantity of data is involved. In particular, it is difficult to show the maximum and minimum ranges of values attained over the entire data span, or any portion thereof, particularly where multiple display entities are shown. Stock prices, for example, are easily displayed with the value of the stock labeled along a first vertical axis and the time at which the stock is valued along a horizontal axis. In such a representation, however, only a limited number of stocks may be displayed on a single display before the number of stocks being displayed overwhelms the display, thereby making it unreadable. Further, the range of the stock price for a full temporal data span (e.g. for the last ten days) must be made by simultaneously "eyeballing" two range end points along the entire relevant portion of the moving axis, back to the stationary axis. Such a method of displaying data is inherently difficult to read and interpret.
A number of improved, computerized applications for displaying dynamic electronic data have been demonstrated. Most of these apparatus and methods, however, have approached the electronic display of such data in a manner similar to the previous paper-based apparatus and methods. In the graphical display of stock quotes, the price of individual stocks for each day is displayed along the vertical axis with the date and time for the particular value of the stock being indicated along the horizontal axis. Within each time segment, the variation of the price of the stock is represented by a single vertical bar, the end points of which denote the high and low values of the stock during that time period. These vertical bars are connected by horizontal bars that link the successive time periods, thereby creating a jagged edged representation of the rise and fall of the stock price over the full time period. In this representation, however, only one stock is capable of being conveniently displayed within the display area, since the vertical bars for different stocks are difficult to distinguish during each time period. Numerous minor modifications to the graphic representation may be made, such as the conversion of vertical lines for each time period to "solid" vertical "candles". However, the line density of these alternative graphical representations also precludes the intelligible display of numerous stock prices on a single display. Display congestion may result from the simultaneous display of multiple stocks. Multiple stocks which do not change appreciably over time hover around the 0% change indicated on the vertical axis. In this display, individual stock values are generally unreadable where they all converge around the same value.
Numerous other variations of computerized display apparatus and methods are also known. Bar charts, showing three dimensional, block-like electronic representations of time varying data can be shown in a bar chart form. In this format, a number of entities within each time period are indicated by solid, colored vertical bars. Other multiple entity electronic displays include pie charts, XY charts (in which one or more data sets are rendered as a series of unique symbols connected by lines within a two-axis, display area) and strip charts (in which the horizontal axis is divided into slots and each slot is occupied by the graphical representation of an entity's data value measured along the vertical axis for the particular slot (e.g. time period). However, as with the above-mentioned stock charts, a limited number of entities can be displayed with any of these charts before the display area becomes unintelligible.
A "box and whiskers" chart may also be used to graphically display electronic data. In the "box and whiskers" chart, the following data are displayed for each entity: a minimum data point, a maximum data point, various percentile indicators for the data within the range of the minimum and maximum, and outliers (i.e. statistically errant data). The data set and the above-listed display points for each entity can be shown as locations along a horizontal bar or line wherein the values for the data are displayed along the horizontal axis and the multiple display entities are stacked along the vertical axis. Once again, however, the "box and whiskers" becomes congested as the number of displayed entities is increased.
Various three-dimensional, graphical displays are also possible with present computer display technologies. One such representation is a cube-like, three-dimensional representation of data. In this representation, one horizontal axis is provided to order the entities and a second axis is provided to show one measure for the entities. Each entity is represented by a vertical bar (i.e. a third, vertical axis) which indicates a second value for the entity. Three-dimensional graphical representations may also be used to display varying data as an undulating "surface". Each of these three-dimensional, graphical representations, however, suffers the same limitations as the two-dimensional representations in that only a limited number of entities may be displayed within the display area before the display becomes congested.
Therefore, the need exists for apparatus and methods for achieving a compact, electronic, graphical display of dynamic electronic data in which numerous entities may be simultaneously displayed. Ideally, such a display would coordinate the layout of the graphical entities for ease of comparison as among themselves, as well as for comparison of each display entity along the "dynamic axis".
Additionally, it is an object of this invention to provide apparatus and methods for electronically displaying dynamic data in which the data is represented by data slices along a continuum and is sequentially presented to the computer display so as to illustrate the variation of the dynamic data for numerous entities over the continuum.